This invention relates to chemical intermediates useful in the preparation of cephalosporin antibiotic compounds. It further relates to a process for the preparation of certain cephalosporin antibiotics. In particular, this invention relates to sodium 3- or 4-(trimethylsilyloxy)-phenylglycinate as the enamine formed with methyl or ethyl acetoacetate and to a process for the preparation of 3-heterocyclic-thiomethyl-substituted cephalosporins such as 7-(3- or 4-hydroxyphenylglycylamido)-3-(1-methyl-1H-tetrazole-5-thiomethyl)-3-cephe m-4-carboxylic acid and 7-(3-or 4-hydroxphenylglycylamido)-3-(5-methyl-1,3,4-thiadiazole-2-ylthiomethyl)-3 -cephem-4-carboxylic acid. The compounds prepared by the process of this invention have been previously described, for example, by Ryan in U.S. Pat. No. 3,641, 021, by Dunn, et al., in U.S. Pat. Nos. 3,867,380 and 3,855,213 and by Cooper in co-pending application Ser. No. 498,886 now U.S. Pat. 3,946,003.
The trimethylsilyloxy-enamine-protected hydroxy substituted phenylglycines described herein are useful intermediates in the process of this invention.